Keg Line Length Balancing – The Science of Draft Beer

This week we take a look at the science behind designing a good draft beer system for your kegged homebrew. Everyone loves draft beer, and I consider my keg system to be one of the best purchases I’ve made in my brewing career. Kegging makes everything easier, and if you want to start kegging, please read my earlier article on how to keg. This week we’re going to look at the more advanced topic of balancing your keg lines.

In my previous article we covered how the temperature of the beer and carbonation level desired in volumes of CO2 drives the overall carbonation pressure – a number you can also calculate easily using BeerSmith. You will need to know your keg pressure as a starting point for designing your overall system. However this is not the complete story – as the lines of your keg play a very important role. In general the longer your keg lines are, the lower the serving pressure at the tap. If the tap pressure is too high or too low, the overall system is said to be out of balance and your beer will either foam or be flat.

Line Resistance is Not Futile

So how does one design a draft beer system to maintain proper balance at the tap? The pressure drop depends on resistance in the beer line. Beer lines have two types of resistance – one due to elevation change (i.e. the keg being higher or lower than the tap), and a second due to the beer lines themselves which generate friction as the beer flows through the lines.

Lets look at resistance first to keep things simple. Here are some sample resistance ratings for various popular beer lines:

3/16″ ID vinyl tubing = 3 psi/ft

1/4″ ID vinyl tubing = 0.85 psi/ft

3/16″ ID Polyethylene tubing = 2.2 psi/ft

1/4″ ID Polyethylene tubing = 0.5 psi/ft

3/8″ OD Stainless tubing = 0.2 psi/ft

5/16″ OD Stainless tubing = 0.5 psi/ft

1/4″ OD Stainless tubing = 2 psi/ft

Generally plastic tube of smaller than 3/16″ ID is not recommended – it provides too much resistance for practical use!

So now that we have the resistance factors how to we go about designing a keg system that is in balance? For the purpose of our example lets assume that you have pressurized your kegging system at a nominal 12 psi, which at a 40F refrigerator temperature represents a mid range carbonation level of about 2.5 volumes of CO2 – typical for an average American or European beer.

At the tap end of our balanced keg system we want a slight positive pressure to push the beer out, but not enough to foam. Generally this would be between less than 1 psi. So let’s target a tap end pressure of 1 psi. The math from here is pretty easy to calculate the balanced line length (L):

L = (keg_pressure – 1 psi) / Resistance

So starting with our example of 12 psi keg pressure, and some typical 3/16″ vinyl keg tubing (which loses 3 lb/ft) we get L= (12-1)/3 which is 3.66 feet. So a 12 psi kegging system would provide 1 psi of pressure at the tap with 3.66 feet of tubing.

Note that some authors leave out the 1 psi tap pressure (i.e. use zero tap pressure) and simplify the equation to L= (keg_pressure/Resistance) which makes the math even easier (the simplified equation would give you 4 feet of tubing vs 3.66 ft). The truth is that you can target anywhere between zero and 1 psi at the tap and still be in balance – the difference is relatively small, though a slight positive keg pressure will give you a better flow rate.

The four foot example with 3/16″ ID vinyl is great if we only have a few feet to go (i.e. in a fridge) but what if one needs to go further? A simple switch to 1/4″ ID vinyl tubing will get us there – looking at the same 12 psi keg system we get: L = (12-1)/0.85 = 12.9 feet. So with the larger tubing we can deliver our beer to just under 13 feet. For other applications we can consider polyethylene or stainless. However if going a long distance one needs to also consider refrigeration – as you don’t want a large volume of warm beer in the lines.

Beer Line Length and Elevation

Changes in elevation also come into play if you design a more complex serving system. The rule of thumb is that your beer loses 0.5 psi/foot of elevation gain. So if your tap is 1 foot higher than the keg it loses 0.5 psi, and conversely if it is lower than the keg it will gain 0.5 psi per foot of elevation.

So if we roll this into our equation, we get the following for a given height (Height – in feet) of the tap above the keg itself:

L = (keg_pressure – 1 – (Height/2)) / Resistance

So lets go back to our original example of a 12 psi keg pressure, 3/16″ ID vinyl tubing and this time put the tap 2 feet above the keg itself. We get L=(12-1-(2/2))/3 which is 10/3 or a line length of 3.33 feet.

Another example with longer lines: 12 psi keg pressure, 1/4″ ID vinyl and a tap four feet above the keg gives: L=(12-1-(4/2)/0.85 which is 9/0.85 or 10.6 feet of line length.

Thanks!

Using the above equations, it is pretty easy to calculate the ideal line lengths for a given keg system operating at pressure. Hopefully this will help you properly balance your own keg system for home use. I intend to roll the line length calculator into a future update for BeerSmith. I hope you enjoyed this short article on balancing your kegging system. Thank you for joining me on the BeerSmith blog – and please subscribe to my newsletter or give my home brewing software a spin for some great ways to improve your homebrewing.

Great article, Brad. I just wanted to point out a couple small errors or typos:

– “Generally plastic tube of greater than 3/16″ ID is not recommended – it provides too much resistance for practical use!” I think you mean less than 3/16″. Resistance per foot increases as diameter decreases.

– “A simple switch to 1/4″ ID vinyl tubing will get us there – looking at the same 12 psi keg system we get: L = (12-1)/0.85 = 12.9 feet. So with the smaller tubing we can deliver our beer to just under 13 feet.” I think you mean “with the larger tubing.” 1/4″ tubing is larger than 3/16″ tubing.

Nice article, but what about 1/8″ line. I actually use it in my kegerator for soda. I am currently running my soda (and seltzer) at 30PSI @ 40F with a 4′ 1/8″ Vinyl Line. It yields a very nice pour and doesn’t leave a pile of line in my fridge.

I don’t know where everyone is getting these numbers. I’ve had a kegging system for 10 years and the math doesn’t match my experience at all.

I’m using 3/16″ tubing and 12psi on the keg. Now, if what I read above is to be believed, if the line is more than 5 feet long, I shouldn’t be able to get beer out the other end. In fact going by math alone, it should suck air backwards up the line since my serving line is just over 12feet long.

In reality, I get a full pint in about 9 seconds with minimal foaming. Shorter line lengths do not work – I will get nothing but foam. I can’t say what the difference is, but I’ve been reading this advice for years and it just doesn’t match my system at all. I’ve even used different kinds of plastic serving line and it didn’t make much of a difference.

I’ve seen alot of variation in serving pressure from 0 to 5 psi (BYO) with words about preference etc. I think 1 psi sounds right and is typical homebrew as we don’t care about speed and have beer that can foam abit more than commercial beers

What about the pressure drop in the stainless tube in the corny keg, this is about 2 ft long and 1/4inch (3/16?) or so, i assume that would aslo add a few psi drop (for corny keg users).

One final note, BYO mentioned a .5 psi drop for a picnic (cobra) style tap.

What do you do if you need a longer line, and can’t afford stainless steel piping, 12 feet doesn’t sound like a lot. Say you have a beer cellar with your refrigerator system and a pub in the attic, you kick up the keg pressure I suppose?

Hi,
I have not done the math in metric, but it should be simply a matter of applying the right unit conversions first. You could use the unit converters in BeerSmith to do it.

For very long lines you need to go to larger diameter tubing, which will have less line resistance. This is better than increasing keg pressure which would lead to improper carbonation for the beer, and subsequently poor carbonation at the tap. A secondary consideration with really long lines is the fact that you need to keep them clean and cool – as they could contain a significant volume of beer.

According to the math I can’t get where I need to. I know I need larger tubing to get the balance, but I am having trouble finding figures for resistance in larger than 1/4″ polyethylene tubing. Where can I find this information?

Hi, I’m just wondering, will The system work without having the system ‘balanced’, with the line I’ve got and height etc it’d have to be about 20 feet long. Is there a way to work out the pressure I should pour at untill I can buy smaller line?
also should I be turning the pressure back up (or down) to carbonating pressure once I have finished a drinking session?
Cheers

If you have flow control you can adjust the flow rate to match your desired carbonation level. Balancing the lines is still important, but you can probably set them a bit on the higher pressure side since you can adjust the valve on the tap to suit your preferences.

Great article. I’m surprised that I haven’t seen any Jockey Boxers chime in yet. I’m currently using, and will be for a fall party, a jockey-box with my home-brewed Cony kegs. Lets tackle my main issue currently. I am using a 150′ coiled SS line to cool the beer as its served. Should I really be using 70 psi to serve my beer correctly?

Second is, I am adding another coil to the box but its shorter? Is this not gonna work at all?

I am finding conflicting information on what the correct resistance for 3/8″ od ss beer line is, and 3/8″ I’d vinyl line is. I have done a lot of research online and have came up with numbers from .09psi/ft to .2psi/ft for the SS and .1 to .3psi/ft for vinyl.

These little differences turn into monumental differences when multiplying them by 100ft of tubing.

How does this translate for Nitro systems? Euro taps with restrictor plates have a higher pour resistance, but I don’t know what that resistance is. Is there some way to measure the pour resistance of a restrictor plate tap?

I built a bar in my basement and want to have my home brews on tap. My chest freezer kegerator will be in the unfinished area of my basement, about 50 feet from the beer tower on top the bar. Here’s what I have done. I ran 3″ PVC for the freezer to the beer tower area and looped back around to the freezer. The 3 1/2 ID beer lines run through one side of the PVC to the beer tower. My plan is to install a blower fan on the other side of the PVC loop and have it blow into the freezer. The idea is that the fan will cause cold freezer air to be sucked in trough the side of the PVC loop where the beer lines are ran and keep the cool. I also insulated the heck out of all the PVC. Is my idea sound? Do you guys think it will work or can you offer better suggestions

@Bt I haven’t actually had to make a run like that, but you might want to look into something akin to the multi-tap bundled and insulated glycol cooled lines that they use for commercial installations. You’ll get better cooling from conduction via the integrated glycol circulation tubes compared to convection with an air cooling system. There’s an example of the bundles I’m referring to in Accuflex’s catalog here: http://www.accuflex.com/images/Acrobat/UltraCat.pdf

I am trying to pump kegged coffee up to a tower faucet in my coffee shop from the first floor. Will nitrogen be sufficient when running pipes up one floor(8ft floor to ceiling), and horizontal to the tower faucet, about 25ft in total?

Gotta admit – I’ve tried to run the numbers and they don’t match my experience at all and I can’t figure out why. I’ve got a kegerator with 5′ gas and beverage lines (pretty sure 3/16″, definitely poly). So, roughly 30″ corny height, then 5′ tubing (though there is slack, so the rise above the keg is only about 12″). I typically force carbonate with about 12 psi for a week, but once that is done, I serve with only 2-4 psi and get a nice head. What am I missing?

This advice worked for me! Refurbished an older upright fridge kegerator…with my beer at 12 psi, 38-40F temp and lines that accompanied it (right at 3 ft, 3/16″ ID vinyl) I poured about half a pint of foam. I have about 6″ of vertical distance from keg top to tap inlets. So, I took the 3/8″ ID vinyl line from a picnic tap, measured it and cut at 4 feet…installed…and perfecto! Nice pour, a pint in about 10 seconds with a perfectly creamy 1/4″ head. Thanks for the advice!

Served by your own tap is one the pleasure of draft beer. Volumes which is measured for the total amount of Carbon dioxide dissolved in the beer. It should be kept at standard temperature and pressure (STP – (32 F)).

That sounds like a lot of pressure – probably too much for that temperature. You would need to balance the keg line with the keg pressure – do a quick search for “keg line balancing” and I think you’ll find my article on this.

I read the article, and replaced my keggerator lines with three and a half feet of 3/16 id tubing, but still get foaming at the front of the pour, I have flow control faucets and am serving at 10 psi. I previously had a two foot run and had the same issue. After the two foot run, I tried a five foot length and poured nothing but foam, so I switched to a shorter run. As it stands now, I can see co2 rising in the line up to the tower so I’m assuming thats where the foaming is an issue. How can I prevent that? Is it a pressure issue?

I am a draft installer And refrigeration guy. 1 thing you guys are missing. It’s all about the relationship of temperature and pressure. Higher the temp the more restriction and subsequent pressure u need. Altitude also plays a big role. Look up the Denver effect – coors brewing discovered that when they took their rocky mtn beers and pressure requirements down from the mountains. They use 9′ on straight Co2. At lower elevations, their beer turned to whipped cream. Ok- soda water is different from beer, but Co2 will only stay dissolved in a liquid substrate if the pressure and temp are in balance. As the product rises above 38f, the Co2 molecules expand in size and exert greater internal keg pressure. Applied pressure must exceed the natural internal keg pressure and again, depends on temp. And also volumes of Co2 dissolved in your particular beer, which varies if brewed properly by style..
I do this every day and there is much dispute over the restriction value of 3/16″id vinyl or PVC tubing. It used to be 3psi/ft, now many argue it’s 2.2psi/ft. Neither seems to work and when I press the suppliers, no one knows where the values come from because the tubing manufacturers don’t test it for restriction. 1/4″ is .8/ft – 5/16″ is .4 – 3/8″ is .2 for vinyl… poly tubing 1/4″ is .6 – 5/16″ is .2 – 3/8″ is .07/ft…. barrier tubing is as follows – 3/16″ = 2.0/ ft – 1/4″ is .3/ft – 5/16″ is.1/ft – 3/8″ is .06/ ft …. Generally 1/2″id across all variations is considered o.o/ft and is for running a distance of up to 500′ (Stadiums, venues, large ships, etc) Guys, I used to brew when I wasn’t working 100+ hours a week running my business, so I’ve done all aspects + draft technician at a Guinness distributor for 20+ years. Let me just say, balancing, troubleshooting, and installing draught beer is closer to rocket science than anyone realizes and I’m sorry to say, but I’ve never seen any info on any home brewers forum that is remotely close to correct. General rule for BEER, NOT SODA OR SDOA WATER when u are say 1500′ or so above sea level, unless you are dealing with a nitrogenated stout or ale is KEEP YOUR PRODUCT BETWEEN 36f & 38f +/- 1 degree IS OK AND USE STRAIGHT CO2 SET AT 12 – 14PSI AND USE 5′ OF 3/16″id HIGH QUALITY BEVERAGE TUBING AND If you’re tapping a fridge directly with a shank and quality faucet, and you don’t have wild beer, it should pour trouble free. Again, every style of beer is different. GENERALLY speaking, nitro stouts and ales have the lowest specific carbonation rates, then ESB ales, ales, lagers. Pilsners, then wheat beers, gueze, and lambics . GENERALLY SPEAKING. The Home Brewer’s Bible, etc can give more specifics. If you run your beer to a remote tower, it must stay refrigerated all the way to the faucet or temp/pressure will get out of balance and the Co2 will bust out and foam will ensue. If using straight Co2, never exceed 16.5psi unless u are above 5000’altitude. Use the correct combination of tubing to stay around 16.5psi and figure on using a minimum of 3′ when figuring your run. If above 38f temp, use more restriction and increase applied pressure up to 17psi only if beer is stored @ 42f max. If it’s 45, use blended gas and u can hit 40psi (depending on co2/n2 ratio) if beer is over 45, you are screwed. Ice it down. The colder the beer, the more readily it will absorb co2 at lower pressures – colder isn’t always better. 12psi should be the lowest you restrict at for most beers. For rise/fall calculations – add .5 every foot of lift & subtract .5 every foot of drop. Measure from the bottom of the keg to faucet spout for most applications, about 1.5psi.. So, say – 5′ of 3/16″ @ 2.2 lbs/ft + 1.5psi from rise = 12.5+/- a little for keg connectors and shank length variation (btw) 1/4″id shank is best. If you do soda, use pure co2 and much higher pressures and much more restriction to keep it carbonated. Sorry, I don’t have time to go into a lengthy discussion on soda theory and practice… Hope this explains and allows fixes for some of your problems. In closing, IF THE APPLIED PRESSURE TO YOUR KEG DOES NOT EXCEED THE NATURAL INTERNAL KEG PRESSURE BY WAY OF TEMPERATURE AND VOLUMES OF CO2 DISOLVED IN YOUR BEER, YOUR BEER WILL GO FLAT. Nature hates imbalance and if u don’t apply enough positive pressure to exceed natural keg pressure, nature will balance that out by out-gassing the disolved co2 from your beer into the headspace of the keg until everything is at a natural equilibrium again. Seriously, ROCKET SCIENCE guys and gals. I could actually go on for several hours or longer about this stuff, but I have to sleep and work, so I bid you goodnight and good brewing.

Sorry, actually Brad did mention pressure/temperature relationship, but seemed to be just in passing. In reality, it is universally important to so many things. I occasionally set up a system with beer pumps for a beer purists bar where the pump is the motive force and co2 is set at a pressure to maintain the brewers intended specific carbonation rate for that beer. Fun, fun, fun. My apologies to Brad- I was reacting more to the questions and complaints and bragging of the great unwashed wondering why they were having problems. So many reasons, so little time. Restriction, related to pressure, related to temperature, and the condition ofriends the tapping equipment, and oh yeah, is it a bad/spoiled keg and was it even brewed and/carbonated correctly. Was it force carbonated or natural. What, I’m rusty 1 cup of corn sugar if you bottle and only 1/3 cup if you keg. Details, there the Devil lays.

Hey Woody – I have had a similar experience. I switched to longer serving lines and my foaming issues are gone. These calculations sound great, but don’t seem to match my real-world experience. I am running 10 ft 3/16 lines at 10PSI right now on picnic taps as my kegerator refrigeration broke and I had no way to serve. No foam, and no problems with beer reaching the glass. I am going to try 4 ft of 3/16 on my current keezer build with perlick 630ss faucets. I will report back when I have the project complete and let you know how it pours. I wonder if you could have a problem with your ball lock (assuming ball lock) not seating/operating correctly. Check the gaskets and poppits in your posts. They are cheap to replace. In the past I have had CO2 mixing into the beer at the post (I believe) making for crazy foam when I poured. I replaced the gaskets and the shameful waste stopped. I know that if I had 2 ft of 3/16 at 10 PSI the beer would come blasting out of there and would be all foam. Try a 10 ft. length and see what happens.

Hi, glad the discussions are still very much alive, I have a few questions for when using an in-line chiller (such as the Cornelius maxi range) with python cooling all the way to the faucet.
1. Is the length of the chilling coil included in the calculation?
2. Where the chiller is 3/8″ ID and the rest of the beer line is 3/16″, how do you calculated this?
3. Where is it best to have the the chiller, immediately after the beer leaves the keg?